<?php
function callback($buffer) {
    return preg_replace('/\s+/', ' ', $buffer);
}
ob_start("callback");
$cat = $this->cat;

if ($cat) {
?>
<h3><?php echo $cat->admin_title;?></h3>
<p><?php echo $cat->short_description;?></p>
<p><?php echo $cat->description;?></p>
<?php
} // if has cat
ob_end_flush();
?>